Q: I have an antenna question that I am very curious about. I live in Philadelphia and can typically scan 43 channels using an amped Mohu Leaf 50, but the local ABC channel (WPVI) is very shaky. Sometimes, it’s fine. Other times, it’s choppy/pixelated. Still other times, no signal at all.

My question is about when it’s choppy. I can view signal information for each channel as I move up and down the channels. The info includes SNR measured in dB. All 43 channels show modulation of 8VSB, whatever that means.

The info shows that 40 of the 43 channels have SNR of 20 or higher and are very smooth with a status of “Lock.”

Here is the curious behavior. When I move to an ABC channel (6-1, 6-2, or 6-3), the SNR starts at 17.5 but quickly (split second) degrades to 16.5 to 17. Sometimes, the status goes from “Lock” to “Unlock” but only for two or three seconds. For that first split second, though, the image is quite sharp, as well as the audio.

Do you have any idea why the signal is good for that first split second? Is there any way to fool the TV into thinking it’s always in the first split second?

A: The reason the signal goes in and out is most likely due to “multipath issues.” When a TV signal travels, it bounces off things it hits (such as mountains and high buildings), and those bounces can reach your antenna, confusing your TV’s tuner. If your TV tuner picks up multiple bounced signals, it will try to sort out the correct signal from the repeats, but sometimes the overlapping transmissions leave gaps in the signal, and the result is a signal that fluctuates and produces an erratic or choppy TV picture—it comes in clearly one minute as your tuner locks on to a signal, and it drops the next. Weather, seasonal changes, and dense tree leaves between your antenna and the broadcaster can affect these multipath problems.

The best solution is to place your antenna as high as you can, which will help it avoid the bounced signals. Check a service such as AntennaWeb to find out where broadcasters near you are located, and look for obstructions (trees, terrain, buildings, or whatever) between you and the signal. You may need to add a little more cable to your antenna—but don’t go wild, since a very long cable (over 20 feet) can also degrade the signal quality. Moving the antenna close to a window can help, as well, and you can even mount a flat Mohu Leaf antenna directly on your window.

—Grant Clauser

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